JPH0280171A - Method of repairing seal joint - Google Patents

Abstract

PURPOSE: To seal an instrument pressure stub tube penetrating a reactor head member by inserting a collar between the inside of the stub tube and the outside surface of a long narrow member, attaching tiller metal surroundedly around the long narrow member, and heating the filler metal. CONSTITUTION: Nuts 30, 32 are loosened and removed in the axial direction of a compression fitting body 34, which is moved from a stub tube 22, with a compression ferrule 26, 28 ground. In addition, a collar 40 is inserted between the stub tube 22 and a thermocouple body 24, while split rings 44, 46 composed of filler metal are fitted around the thermocouple body 24 and fixed against the flange 42 of the stub tube 22 and the collar 40. With an electric current flowing through the stub tube 22 by means of a heating device, the filler metal melts, flowing towards the stub tube 22, welding and sealing the three, i.e., thermocouple body 24, collar 40 and stub tube 22. The nut 30 is screwed onto the end of a screw 37, and the nut 32 is screwed onto the end of the screw 39 of the fitting body 34.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of repairing seal joints, particularly seal joints for core-through instrumentation elements in nuclear reactors. More specifically, the present invention relates to a pressure stub tube in a nuclear reactor;
The present invention relates to a method of repairing a leak-prone seal joint in which a compression fitting seals between a thermocouple mounted concentrically within the stub tube.

According to the prior art, a sealing fitting for a core-penetrating instrumentation element in a nuclear reactor comprises a compression fitting having a fitting body;
One includes a nut that is screwed into the fitting body and a ferrule that presses against each other in the radial direction, and these ferrules press against each other by tightening the nut to connect the outer pressure stub pipe and the inner diameter of the stub pipe. The thermocouple has a cylindrical surface with an outer diameter smaller than that of the thermocouple.

The portion of the reactor through which the instrumentation elements penetrate is generally the head member of the reactor. During operation of a nuclear reactor, the sealed seam through the head member is exposed to high temperatures, pressures, and nuclear radiation. For this reason, the ferrules for the aforementioned compression fittings are generally manufactured by the Crawford Finting Company of Cleveland, Ohio, U.S.A. under the trademark "
The type sold under the name "Svagelok" or the type sold under the trademark "Ty 1ok" by Tylok International, also located in Cleveland, is used. .

On the other hand, the head member of the nuclear reactor in the installation of at least one nuclear reactor unit is generally penetrated by between 39 and 65 instrumentation elements, each of which is provided with a compression seal seam. And these seal seams often leak, spilling contaminated water into the head area, contaminating this head area and thus making it cumbersome for workers to access this head area, thus impairing their work. There was a problem that the amount of REM increases as the time for which personnel are exposed to radiation increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art.

The present invention particularly relates to leakages created by radial compression fittings between a stainless steel pressure stub tube and a cylindrical stainless steel instrumentation element body, such as the body of a thermocouple, in a nuclear reactor. This invention relates to a method for repairing joints that are subject to seals that are susceptible to damage.

In this case, the thermocouple is generally mounted concentrically within the stub tube by a compression fitting.

The compression fitting then radially clinch both the stub tube and the thermocouple body due to the forward movement of the mounting nut on the ferrule fitting body, i.e. the swaging action of the ferrule caused by the tightening of the mounting nut. It has compression means.

Therefore, the novel method of the present invention for repairing such leak-prone compression seal fittings includes the steps of loosening the mounting nut and removing it axially from the compression fitting body, and removing the ferrule from the thermocouple fitting. removing the book by gliding; inserting a split collar or ring between the inside of the stub tube and the outside of the cylindrical body of the thermocouple; and cleaning the surface to be sealed.
attaching a split ring of braze material to surround the thermocouple body adjacent the exposed end of the stub tube and the collar; heating the braze material by electrical resistance heating of the stub tube; repositioning and assembling the nut to complete the repair of the seal joint.

DESCRIPTION OF PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

In FIG. 1, numeral 10 generally indicates a pressurized water reactor (PWR) having a head member 12 bolted to the top of a main vessel 14. An inlet nozzle 16 and an outlet nozzle 18 provided in the main vessel 14 are connected to a steam generator of a reactor steam supply system.

The main vessel 14 includes a reactor core area 20. which accommodates a plurality of fuel assemblies (not shown). and control element assemblies, flow guiding core barriers, flow skirts and other reactor internal elements not shown, all of which are well known to those skilled in the art of nuclear power generation. It is something.

Thus, in general, both the control element assembly and the instrumentation pressure stub tube 22, which includes an instrumentation element such as a thermocouple 24 whose body is cylindrical in shape, are connected to the head member 1 of the reactor 10.
It is arranged to penetrate through 2. In this case, as shown in FIG. 2, the thermocouple 24 is
” has a body outer diameter that is smaller by the value of .

And according to the initial design of reactor production, stub tube 2
2 and the thermocouple 24 includes a compression fitting having a fitting body 34 and a mounting nut 3 screwed into both threaded ends 37 and 39 of the fitting body 34, respectively.
0 and 32 and 2 for stub tube 22 and thermocouple 24
and a set of radial compression means.

Each set of radial compression means is connected to the fixture body 34, respectively.
It consists of ferrules 26 and 28 which are tightened by nuts 30 or 32 at each end so as to press into contact.

Compression fitting body 34 has a tapered mouth portion 36 surrounding stub tube 22 and a tapered mouth portion 38 surrounding thermocouple 24 . These tapered nip portions 36 and 3
8, the nuts 30 and 32 are connected to the fixture body 34, respectively.
The ferrules 26 and 28 associated with one of the concentric cylindrical members, i.e. the stub tube 22 or the thermocouple 24, are screwed onto the threaded ends 37 and 39 of the cylindrical member, tightened and advanced along the axial direction. are pressed against each other.

However, during the operation of a nuclear reactor, leakage generally occurs in
This is likely to occur between the ferrules 26 and 28 which are pressed together by the tapered jaw portion 38 of the compression fitting body 34 and are swaged into thermocouple 24 .

The present invention therefore provides a method for repairing such leak-prone seal joints.

According to the method according to the invention, first, the nuts 30 and 32
is loosened and removed axially along both threaded ends 37 and 39 of compression fitting body 34, and fitting body 34 is then moved axially from stub tube 22. The radial compression ferrules 26 and 28 associated with the tapered jaw portion 38 of the fixture body 34 are then crushed out of engagement with the thermocouple 24.

This is then preferably followed by a wire brushing operation to clean the surfaces of the various parts.

Also, a split metal sleeve or collar 40, preferably made of a material having a thickness of "X" and having the same coefficient of thermal expansion as the stub tube 22 and thermocouple 24, inserted in between.

The stub tube 22 and thermocouple 24 are typically made of 5US304 stainless steel and are preferably made of 5O8 stainless steel.
304 stainless steel is selected as the material for the split collar 40. The material of this color 40 is Color 40
It must be possible to widen the split to provide a passage for the thermocouple 24 through this section.

Collar 40 is then removably inserted into stub tube 22. In this case, preferably color 40
is secured to the end face of the stub tube 22 by an outwardly facing stop flange 42 on the collar 40. This stop flange 42 connects the collar 40 into the stub tube 22.
Limit the amount of axial insertion.

Additionally, split rings 44 and 46 made of a wax material.
are each fitted around the thermocouple 24 and then moved axially and secured against the stub tube 22 and flange 42 of the collar 40.

A current is then passed through the stub tube 22 using a two spaced electrode type electrical resistance heater or other suitable heating device, such that the area adjacent the end of the stub tube 22 is cherry red in color. , i.e. about tooo℃
(approximately 1850'F).

This causes the brazing material, such as an alloy of substantially 82% gold and 18% nickel by weight, to melt and flow toward the heated stub tube 22, the thermocouple 24,
The collar 40 and the stub pipe 22 are welded and sealed.

After this weld seal is completed, the fitting body 34 is moved axially so that its tapered jaw portion 36 abuts its associated ferrules 26 and 28, and then the nut 30 is threaded onto its threaded end 37. The nut 30 is tightened until the abutting radial compression ferrules 26 and 28 are clinched or secured onto the stub tube 22. Then, the tapered opening portion 38 of the fixture body 34
The previously removed ferrules 26 and 28 associated with
Nut 32 is threaded onto threaded end 39 of fixture body 34 without mounting. This nut 32 merely protects the welded seal portion and limits movement of the fixture body 34.

As is clear from the above description, according to the present invention,
A completely novel seal joint repair method for sealing an instrumentation pressure stub tube through a leak-prone head member in a nuclear reactor is provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a nuclear reactor showing a reactor head member having a plurality of instrumentation element penetration parts in a nuclear reactor to which the present invention is applied. FIG. 2 is an enlarged detailed cross-sectional view taken along line 2-2 of FIG. 1, showing a pressure stub pipe extending through the reactor head member shown in FIG. It is a joint that seals between thermocouples, and shows the state of the seal joint after it has been repaired by the method of the present invention. IO...pressurized water reactor, I2...head member, 14...
・Main container, 16... Inlet nozzle, 18... Outlet nozzle,
20...Core area, 22...Stub tube, 24...Thermocouple, 26.28...Ferrule, 30.32...Nut,
34...Compression fitting main body, 36.38...Tapered bind-off part, 37.39...Threaded end, 40...Split sleeve, 42...Split collar, 44...Split collar (brazing material).

Claims (1)

[Claims] A fitting for sealing between a stub tube and an elongated member concentrically mounted within the stub tube and having a cylindrical surface with an outer diameter smaller than the inner diameter of the stub tube, the fitting comprising:
a compression fitting having a fitting body; a mounting nut means;
radial compression means, the steps of: loosening and axially removing the mounting nut means from the fitting body; and removing the radial compression means from the elongate member. inserting a collar between the interior of the stub tube and the outer surface of the elongate member; and attaching a braze material adjacent the end of the stub tube and surrounding the elongate member; heating the braze material to form a welded seal; and axially returning the mounting nut means to attach it to the fixture body, completing the repair of the seal joint. How to repair fittings.